1. Field of the Invention
The present invention is in the field of radio and specifically relates to apparatus and a method for simultaneously generating a set of carriers having all of the possible station frequencies within the frequency modulation (FM) broadcast band and for simultaneously modulating all of the carriers with an audio, video, or digital signal.
2. Background and Prior Art
In the United States, the FM broadcast band is approximately 20 MHz wide, and extends from approximately 88.0 MHz to approximately 108.0 MHz. Assignable station frequencies are spaced uniformly across this band and are separated by 200 KHz at the so called "odd frequencies" such as 90.1, 90.3, 90.5 MHz, etc. A significant aspect of the present invention is the simultaneous generation of all of these frequencies with relatively simple apparatus.
In the United States, to prevent interference, the frequencies in any particular geographical area are allocated by the Federal Communications Commission from among the assignable frequencies in the FM broadcast band.
The present invention could be used in providing an emergency message that can be detected by an ordinary FM receiver regardless of which station the receiver may be tuned to. The circuit of the present invention could also be used to provide digital transmission over a wide band, thereby making jamming or interference difficult. In yet another application, the circuit of the present invention could be used in television or microwave repeaters where there is a need for keeping a particular modulation while changing the carrier frequency to avoid feedback.
In principle, the purpose of the present invention could be accomplished by providing approximately 100 oscillators, each operating at one of the assignable frequencies, and by frequency modulating the oscillators with a common modulation signal. However, this approach is undesirable because of the large physical space required and because of the cost. The present inventor has found a simpler and better way of achieving the desired result.